Translucent metallic enamel and a process of making it



y 1952 R. E. PIKE 2,604,414

TRANSLUCENT METALLIC ENAMEL. AND A PRoc ss OF MAKING IT Filed Sept. 30, 1945 FIG. I. FIG. 2.

RED

PURPLE CHROMA HUE BLUE GREEN YELLOW INVENTOR. RALPH E. PIKE EL L ATTORNEY Patented July 22, 1952 UNITED. STATES a r 2,604,414- TRANSLUCENT'YMETALLIC ENAMEL AND A Q Y PROCESS OF MAKING rr- 7 Ralph E. Pike, Media, Pa., assignor to E. I. as

Pont de Nemours & Company, Wilmingto'uy; Del., a corporation of Delaware Application September 30, 1948, Serial No. 51,883

1'7 Claims.

' This invention relates to lacquers and synthetic enamels and particularly to such coating compositions which possess a translucent metallic'appe'arance and whioh are currently popular for automobile finishing.

A customary requirement for coating compositions is" opacityin relatively thin films, a property "commonly referred to as hiding power. Although desirable in some of its aspects, this opacity limits'the appearance of a film of coating composition to the colors reflected from its surface. In the past few years, coating compositions which have a transparent appearance and relatively low hiding power, but which possess a desirable depth, luster, and metallic appearance, have been very popular, particularly as automobile finishes. In this case depth does not involve intensity as in the term deep color. Rather, it means the optical illusion of distance or thickness characteristic of metallic finishes. The metallic appearance "is difiicult to describe, but it' might be regarded as the optical sensation resulting from the multicolor eirect produced by a; somewhat translucent coatin composition partly by the light refiectedfro'm the surface, and partly by the light transmitted by the-translucent film and ultimately reflected by aluminum flakes in the film.

A coating composition described as being metallicin appearance possesses the following characteristics, to some degree, simultaneously: (1) An appearance of depth or distance in the film, (2) An ability to change color dependingon the nature and direction of the illuminating source, (3) The ability to highlight, or attract attention to, changes in contourof the finished article (for instance, body design of automobiles), and

(4) a multi-colorior polychromatic effect on flat surfaces. Thus, it is common inthe coating composition industry to refer to overallvmetallic effect rather than to attempt to identify the specific quality thatis present or absent. Since no composition is known which possesses a maximum of all four characteristics, useful coating compositions are selected on the basis of the most favorable combination of those characteristics. In the description of this invention the terms for the qualities of color will be based upon the definitions given in the Munsell Book of Color' describe means of-accomplishing some degree of transparency in nitrocellulose lacquer andsyn- 'thetic' enamel compositions Essentially these methods'retainjthe principal pigment in astate of very fine divisionso that its transparent properties may be utilized, in conjunction with aluminum flakes,- to produce the above-mentioned minum'fiake cause quuin and alu rni u-"m ca 2- desirable metallic appearance. -U. S. Patent 2,140,745 covers the process of fiushin'gf .pigments from the wet pulp stage directly in'tduniforni dispersion in lacquers Without the interrnediate steps of drying and pulverizing' the' pigmerit; While applicable to some degree warren pigments, the process is most useful Withthose or+ dinarilymanufactured by chemical precipitation from water solution. U. S. Patents-2 ,335,7-and 2,384,579 prepare iron oxide pigments capable of being fiushed into lacquer or enamel vehicles'so that the very small primar particles of the-pigsment do not agglomerate to any marked extent and so that th'e nature of the particles is not substantially changed-from their freshly-precipitate'd condition. 'Ihus', durable, lightfast and relatively inexpensive pigments or comparatively high'transpare'ncy and" low hidingpoweriare made available for use as the principal, or socalled prime pigment in lacquers and synthetic enamels for outdoor exposure. In low concentrations these colloidal hydrated or hydrous ferric oxides impart an amber tinge to the filmforming component of the coating compositions. In higher concentrations, the color is a translucent go'ld, brown, or reddish brown. In the actual use of the ironoxides, it has beennecessary and desirable to add to the iron oxide base composition closely controlled amounts of selectedrelatively opaque tinting or toning pigments, suitably dispersed in a useful vehicle,- to impart opacity or hiding power, at the same time coloring the com-position to the desired hue. Small quantities ofselected flaked aluminum pigment added to this mixture increase the value or lightness of the color and provide the'meta'll ic appearance. However,- when these hydrous "iron oxidebases' are shadedby orthodox'methods using conventional pigme'nts-black, white,maroon, blue," green and yelloweither oi two things occurs: (1) so little shadingipigmentis used that the hiding "poweris insufiicient or an amber or brownish tone from the hydrous iron oxide is Visible, li miti ligthe" c0101" range of finished compositions to browns and olive greens; (2) So much shading pigment is used that the-excellent outdoor durability-of the hydrous iron oxide in the coating composition is overcome bythe co'mparatively'poor outdoordurabi-lity of the shading pigments,which" in most cases are notably inferlor I to' hydrous iron oxide in' color-fastness, challe-I'esis'tance, and general resistance to' fil'rh deterioration. For instance, excessive amounts of ph'tha'locyan'ine blue and green pigments,

while providing satisfactory light stability, produce a--d1'1ll i r'edhall: or bronze under normal exposure condi 's. Ekcessiveain ts of in'g. =Carbon' black and lamp"- black pig ehts} the low -tintin'gstren'gth t pe required to maintain- 10w aluminum -concentration, 'show' e'arl y dulling and chalkingxon exposure. 1 J In order to obtain maximum'freedom from-alu- 3 minum mottling or flooding (heterogeneous pigment pattern in the applied film) in practical metallic enamel formulations, a minimum concentration of aluminum in the enamel is essential. Unfortunately, brightness and lightness increase with aluminum content, and the bright colors are currently the most popular ones for articles commonl finished with metallic colors. These bright colors can be made by any of the following methods.

A. Use of high aluminum concentration resulting in severe flooding or mottling tendencies and early dulling on exposure.

B. Use of a combination of aluminum and nonchalking opaque white pigments, which invariably results in a sacrifice in metallic appearance ov'er alternate A.

C. Use or a maximum of low tinting strength, transparent type pigment and a minimum of strong toning pigments, by the complementary blending principles as described in this invention.

It has been desirable to prepare enamels and lacquers with a greater variety of hues, improved metallic appearance, and improved outdoor durability, using the iron oxides of U. S. Patents 2,335,760 and 2,384,579. It has also been desirable to accomplish essentially the same results by finding and using, as additives" to or substitutes for the hydrous iron oxides, prime pigments which possess the desirable properties of transparency, low tinting strength, and good durability, capable of being tinted to the desired hue with relatively minor quantities of light-fast toning pigments that are strong (high in chroma), relatively opaque, high in tinting strength, and that preferably but not necessarily possess good durability in enamel films.

Accordingly, the purpose of this invention is to provide improved synthetic enamels and lacquers which are durable, lustrous, translucent and metallic in appearance. A further object is to make new durable, relatively inexpensive colored coating compositions, suitable for finishing automobile exteriors, which possess metallic effeet to an unusual degree. Another object is to make durable gray lacquers or enamels without the use of black or white pigments. Still another object is to make a pigmented composition of a specific 'hue using a pigment of that hue or an equivalent blend of more than one pigment in only minor portions with respect to the total pigment present. An additional object of this invention is to provide a method of using the desirable properties of hydrated iron oxide pigments in enamels and lacquers possessing better durability and a wider variety of hues than heretofore available. Other objects will appear as the invention is described.

' There are no known pigments which individually impart all the desired properties discussed above to a synthetic resin metallic enamel, but by selecting pigments according to the new procedure of the present invention, pigments which otherwise are undesirable can be combined to produce brilliant, durable beautiful metallic finishes which are substantially non-chalking, and

non-fading.

The objects of this invention are accomplished fundamentally by using the hydrous iron oxide pigments described in US. Patents 2,335,760 and 2,384,579 in combination with one pigment, ora

blend of two pigments, relatively complementary to the iron pigment so that the yellow nature of the latter is substantiall neutralized to a true gray or to a grayish base of the same hue as that desired in the final color. Then a tinting pigment of that hue, but of higher chroma, or an equivalent blend of two or more pigments, is added to adjust the color Of the product to the desired strength, or chroma. A preferred modification is to select the neutralizing pigment (or pigments) in such a way that it (or one of them) can be used in excess of the required neutralizing quantity to produce the desired color. This method reduces the number of pigments required and simplifies the application of this invention to commercial enamel manufacture. Finally, the value or lightness is adjusted by adding flaked aluminum pigment. The resulting composition possesses simultaneously the desired hue, chroma, and value along with the most favorable combination of the four characteristics of a metallic enamel: depth, apparent color change, high lighting, and polychromatic effect. While the above description is based on hydrous iron oxide pigments, the same principle is applicable to other prime pigment bases, as will be explained later.

In the attached drawing, Figure 1 shows the three dimensional diagrammatical concept of color characteristics. The vertical axis is value (from black to white), the horizontal axis is chroma (from neutral gray at the center to stronger color away from the center) and the radial or angular location on any given value plane is hue. Figure 2 is a vertical view of the same system, a two dimensional view showing only hue and chroma, the qualities most important in this invention. The numbered positions on Figure 2 show the approximate hue and chroma of the eight pertinent pigments. Figures 3 and 4 are vertical diagrammatic views similar to Figure 2 and are described more fully hereinafter.

It is to be understood that throughout the examples, the pigments are in the form of mill bases prepared by dispersing the pigment in a suitable vehicle by grinding in a ball-, roller-, pebble-, or buhrstonemill, by other suitable dispersing methods, or in some cases by the processes of U. S. Patents 2,140,745 and 2,384,579.

TABLE 1 Pigment key Pigment Description Hydrous Iron Oxide (Note 1) U. S. P. 2,384,579. Lake of dichloro-isodibenzanthrone on Barium Rosinate.

Phthalocyanine Blue.

Phthalocyam'ne Green.

Chromium 'letrahydroxide (Guignet's Green).

Lightiast Nickel Azo Salt, the nickel complex of the azo dyeobtained by coupling diazotized parachloraniline with 2,4dihydroxyquinoline, U. S. P 2,396,327; claim 5.

Extra Fine Aluminum Flake in Mineral Spirits) (Notes 1, 2). Coarse Aluminum Flake (75% in Mineral Spirits) Fins Aluminum Flake in Mineral Spirits) (Notes 1, 3)

- etc 1).

Medium Particle Size Channel Carbon Black. Lamp B ck. Ferrite Yellow Orange. Synthetic Red Iron Oxide. 40% Ponsol Blue Lake. Miio -i Blue (Ferric Ferrocyanide). Precipitated Hydrous Iron Oxide (Water Wet) (N etc 1) U S. P. 2,335,760. (17) Vat Thioindigoid Dyestufi-Indo Maroon.

N orn lIn all the enamel compositions of the examples, the percentage oi pigment is on a pigment solids basis.

NQTE 2I ig ment 7 can further be described as an "extra fine aluminum hning paste (non-leafing), in which substantially no flakes are as large as 20 microns in diameter and substantially all oi the flakes are less than 10 microns in diameter.

NOTE 3-Pigment 8 can further be described as a "standard aluminum paste (leaflng)," in which about 40% 01 the total surface area is composed of flakes with a diameter larger than 20 microns.

In Table 1 pigment I is a prime or transparent base pigment composed of iron oxide in chemical combination with water, an example of which is disclosed in U. S. Patent 2,384,579. Pigments 5 and 6 are prime pigments possessing qualities comparable to prime pigment I in durability, lightfastness, transparency, and tinting strength. Hence they are substantially equivalent to pigment #I in the principle of this invention, but being different in hue andchroma, they produce different families of colorswhen substituted for pigment #I. Pigment I6 is similar to I but is prepared according to U. S. Patent 2,335,760. In the claims the term hydrous iron oxide is intended to refer to pigments substantially equivalent to those prepared according toeither of the patents just mentioned above. Pigments 2, 3 and 4 are tinting or toning pigments possessing high tinting strength, high chroma, lightfastness, and reasonably good outdoor durability.

A durable transparent metallic neutral gray without black or white pigment will serve as a fundamental example of an automotive enamel of this invention. In this case it is desired to neutralize the hue and chroma of pigment I, yet retain a preponderant proportion of pi ment I in the finished enamel in order to utilize its transparency and durability to an optimum degree. Figure 3 is a graphical representation of the pigmentation. Sincethere is no known pigment completely complementary to pigment I. proportions of 2 and 4 are blended to produce an intermediate hue I8, which is substantially complementary to I. Then blend I8 and pigment I are blended in the proper proportions to produce I9, a neutral gray possessing substantially no hue or chroma. Pigment 3 might be substituted for pigment 4. A blend of 2 and 3, complementary to I, would have a higher chroma than blend I8 and would require larger proportions of pigment I to produce a neutral gray.

metallic efiect than the same color gray enamel made with pigments I, 2 and 4. In either case, a small amount of a flaked aluminum pigment is added. This lightens the color to the desired. value and contributes to the metallic eiTect.

The final steps in producing a finished enamelare reduction to the desired pigment to hinder ratio with additional vehicle, introduction of driers and other modifiers, and adjustment to the desired viscosity with suitable solvents.

The method of this invention for pigmenting an enamel possessing hue. and chroma, as contrasted with a neutral gray, is described as follows for a grayish blue metallic enamel. The desired hue and chroma were selected and are represented by the point, 2E) on Figure 4. To arrive at this hue and chroma,'pigments 2 and 3 are blended in proportions yielding blend 2| which is complementary to pigment I. Blend 2| and pigment I are mixed in proportions yielding blend 22 which is on an extension of a straight line connecting 2 and 20, so that by adding pigment 2 to blend 22 in small increments color 20 is approached and reached.

While the theory of producing a durable gray and a grayish blue metallic enamel have been explained above, the invention will be more completely understood from the examples listed in Table 2, in "which the parts are by weight. The examples are largely shown in tabular form for convenience of comparison. The column or row headings are identified as follows:

Complementary Blend is blend of pigments to produce an improved metallic enamel of a desiredcolor by this invention.

Conventional Blends I and II are alternative blends of conventional pigments commonly used in metallic enamels of the same color as the corresponding Complementary enamel. Two alternatives are given for comparativepurposes. For instance, Color #13 Gray is substantially the same color in its three modifications, namely;

The enamel thus produced would possess greater Co p y. COIlVentiOnal d C ventransparency, less hiding power, and a different tional II.

TABLE 2 Metallic enamel compositions Complementary Blend Conventional Blend I Conventional Blend 11 Matched Color Pigment Pigment Pigment P/B P/B P/B Ratio Ratio Ratio No, Color Per Cent; No. Color Per Cent No. Color Per Cent 11 (11 Black a0 (10 Black 13 6 (14) Blue 30 11 53 (A) Gray 9'2/100 (7) Aluminum 30 8'7/100 (7) Aluminum... 40 9'9/100 7) Aluminum 6g Tot-. 1 Total 100 Total :51

510) Black 1s (10) Black 25 Tr (B) Gray 9.3/100 10. 2/100 9. 0 100 I g 10) Black 12 (C) Green-Gray 9.4 100 9.6/100 11. 6/100 fi fg I '7 Total T00 8 (14) Blue"; c1 6) Yellow .IIII 0) Black 12 21535156121" "s (13) Bme'Gmym Emmummumm" 30 83/100 (9 Aluminum 44 96/100 9 Aluminum Total Total 100 (E) o 8. 4/100 8. 0/100 $3 fl g g 42 8. s/ oo (3) Total 1o 1 Trace.

tol phthalate resin (solid) V TABLE 2-;-Continued Metallic enamel compositionscontinued Complementary Blend Conventional Blend I Conventional Blend II Matched Color Pigment V Pigment Pigment /B 1 Pl];

' Ratio Ratio Ratio No.ColorPer Cent No.- OolorPer Cent No.-Co1orPer Cent (1) Black a 4 (10) Black 5 e er a a; at a e1 ow l e ow (F) Brown 8.8/100 8.8/100 (9) Aluminum n 31 14.8/100 (9) Aluminum 25 Total 100 Total 100 Total 100 5) Green 61 (11) Black 22 Black 17 (2g g i l 2 g ii g (1 R 2 ue e ow v (G) Grayf 7153/10 8 Aluminum- 23 371/100 8) Aluminum..." '60 94/100 8) Aluminum 81 Total 100 {if Total 100 Total 100 (5) Green. 55 14) Blue s3 15 Blue as e tr e ane- 11 ue ac 1 (H) Blue 12. 3/100 (8) Aluminum 15 100/100 9. 8/100 (8) Aluminum 23 Total i 100 P/B is a designation for the ratio of total pigments to solid vehicle by weight. This refers to the final enamel produced, using the pigment blends in the table. Variations in P/B ratio occur because each pigment is dispersed (or ground) separately with small quantities of liquid vehicle to produce a mill base. For commercial production reasons, mill bases do not necessarily have the same P/B ratio.

The following formula represents a typical baking enamel vehicle for all of the tabulated pigmentations in which the parts are by weight: 49% linseed oil-China-wcod oil glyceryl phthalate resin (solid) -.2559 52% linseed oil glyceryl phthalate resin The thinner or solvent content of the final enamel is variable because it is common practice to prepare enamels at a uniform viscosityrather than at a constant percent of volatile solvent. Therefore, variations occur from colorto color and often even between different batches of the same enamel. The viscosity of the baking enamels was 37 seconds :4 seconds in a Parlin #10 viscosity cup at 25 C. A suitable baking sched ule for these products applied to metal substrates was 1 hour at 225 F.

The following formula is a typical air drying vehicle for illustrating all-of the tabulated pig (solid) 2.82 50% soya oil-China-wood oil pentaerythritol phthalate resin (solid) 6.88. 33% China-wood oil phenolformaldehyde varnish (solid) 0.41 Drier solution (3% manganese) 0.4.5 Urea-formaldehyde-butanol resin (solid) 1.03 Butanol 0.69 Hydrocarbon solvent (volatile) 62.13

mentations in which the parts are by weight:

49% linseed oil-China-wood oil glyceryl phthalateresin (solid) 25.59 52% linseed oil-glyceryl phthalate resin V V 7 (solid) L- 2.82

50% soyaoil-Chin a-wood oil pentaerythri- 33% China-wood oil phenolformaldehyde varnish (solid) 0.41 Drier solution (16% lead) 0.68 Drier solution (3% manganese) 0.46 Drier solution (2% cobalt) 0.91 Hydrocarbon solvent (volatile) 62.25

The final volatile solvent content varied as de scribed under the baking vehicle. The viscosity of the air drying enamels was the same as for the baking enamels.

An example of a finished synthetic resin enamel typical of those intended in this invention, using the above air drying vehicle'as a basis, is as follows. The parts are by weight. The pigmentation is taken from Complementary Color A, Gray, of Table 2:

Pigment 3, Blue 0.454 Pigment 2, Violet 0.247 Pigment I, Yellow 2.167 Pigment 1, Aluminum 1.228

49% linseed oil-China-wood glyceryl -phthalate resin 24.527 52% linseed oil glyceryl phthalate resin 2.701

50% soya oil-China-wood oil pentaerythritol phthalate resin 6.599

33% China-Wood oil phenolformaldehyde varnish (solid) 0.392 Dried solution (16% lead) 0.654 Drier solution (3% manganese) 0.436 Drier solution (2% cobalt) 0.872 Hydrocarbon solvent (volatile) 59.723

In all of the 8 basic colors of Table 2 (A-H), the Complementary modification possessed better application properties, metallic appearance, or outdoor durability, than the two corresponding Conventional enamels. In substantially all instances, the Complementary modification was superior in every respect. In the Complementary enamels, no black or white pigments were used,

the aluminum pigment content was lower, with one exception, and the pigment content was predommately pigments I, 5 or 6 or a combination thereonso that theresulting enamels were superior in application properties, durability and meta-llicappearance. 1

The following are examples of the application The cellulose nitrate in this composition is the conventional lacquer type, having a viscosity of about 6 seconds in Formula C of A. S. T. M. D-801-33.

Brown Lacquer J of Table 2, using this vehicle .be-made with either a baking or an air dry vehicle.

A suitable vehicle for the lacquersin Table 3 has the following analysis, by weight:

' Per cent Cellulose nitrate 1 7.6 50% cocoanutoilglyc'eryl phthalate resin 8.8 Dibutyl phthalate 3.6 Blown c'astoroil 2.5 Butyl acetate 24.3 Methyl ethyl ketone 10.8 Methyl isobutylcarbinol 5.4 Toluene C C 5.1 Xylene r 5.0 Ethyl alcohol 13.5 High solvency naphtha '-3.4

oithis invention to nitrocellulose or lacquer-type 5 compositions. For direct comparison, the pighad the following composition, by weight: mentation of synthetic resin enamels of substan- 1 .tially the same color as the first two lacquers is t '6 H Per (Pent shown. Inall compositions black and white pig- {gmen ye ow ments are absent, and the pigmentvcombinations 10 figment green -----v are based on the principles of this invention. It figment marqon .is to be understood that in the lacquers, as in figment e u m- -r-? the synthetic resin-enamels, .all pigments had Cellulose n t ----.-----=-.-.-,.F -"Pe 17.1 been previously dispersed in a suitable vehicle .COCQfimlt O E YC Y phth la si 3.6 (usuallynitrocellulose for-the lacquers) bymeth- 15 Dibutyl phthalate Y,3.5 odsknowntothe art. Blown castor oil 2.4

TABLE 3 Complementary Blend Nitrocellu- Complementary Blendlsyntl etic lose Lacquer Resin Enamel :Matche'd'Oolor' Pigment Pigment PIB I 'P/B Ratio Ratio No. Color Per Cent No. Color Per Cent (16) Yellow 51.3 (1) Yellow 74.0 V (17) Maroon. 6.9 (2) -Violet 4.0 W W E3? $353505: 32:? 125/100 2%; 2331mm. 13:3 1 Total 100.0 Total 100.0

' (10) Yellow 80.5 (1) Yellow. 85.7 v (17) Maroon 10.4, (3) glue 6.1 (K) Brown.

935/100 E3; $3355.15: iii? (Z; Alfie-:1: 33%

Total 100.0 Total 100.0 (5) Green 68.9 (16) Yellow 11.1 V (17) Maroon.-. 4.2 (L) Gray 113/100v (3) Blue...-.--. 1.4 (8) Aluminum.- 14.4 0

50.2" 4 12.; (M) Gray 8.55/100 1g (5) Green 65.9 (16) Yellow 18.8 (17) Maroon 3.6 (N) Dark Gray 11.3/100 (4) Green 1.1 (8) Aluminum. ll.1

T tal..."- 09:0 710) Yena tq. 81.4 (.3) .Blue-.-..,.-. 10.5 (0) Green 49:1/100 g gfiggfi 2 2 Total I1 00.,0'

In Table v3, the Synthetic Resin Enamels may Butyl acetate 23.6

Methyl et ylketohf uiu; Methylisobutyl carbinol In the claims the term preponderant as applied to the transparent "prime pigment means that it is present in amount greater than any other single pigment. The term transparent pigment refers to a pigment which when dispersed in an organic vehicle has 'low hiding power and transparency as distinguished from a rela# tively opaque pigment with relatively high hiding power. In the former case the transparency of the pigment allows .the light lto reach the alufilms giving them .an unusual apparent depth.

For this reason the standard grade of aluminum paste is preferred in both cellulose derivative and synthetic resin'enamels of this invention where a maximum degree of reflection is desired.

The proportions of pigments may vary to give a large assortment of colors and effects; but in the preferred embodiment of the invention, the prime transparent pigment (A) of the claims may vary between 25% and 85.7% by weight of the total pigment in synthetic resin enamels and between 50.2% and 84.2% for cellulose derivative lacquers. em

The relatively transparent complementary pigments (B) and tinting pigment (C-)of-the claims may vary in the preferred embodiment from 11% to 45% combined in synthetic resin enamels and from 4.7% to 44.6% in cellulose derivative enamels. 1 I

The aluminum powder (D) of theicla'ims may vary from 3.1% to 30% in synthetieresin enamels and from 4.5% to 36.4% in cellulose derivative lacquers.

The principles of pigmentation for coating compositions with a metallic appearance disclosed in this invention are applicable to all types of filmforming materials including, (1) all types of alkyd resins made from any combination of a polyhydric alcohol and a polybasic acid, unmodified with non-drying oils, semi-drying oils, or drying oils such as cocoanut oil, soya oil, and linseed oil, respectively; (2) cellulose derivative film-forming agents; (3) vinyl type materials such as vinyl,

acrylic, and allyl resins; (4) ureaformaldehyde type resins; (5) melamine formaldehyde resins; (6) phenol formaldehyde resins and oleoresinous compositions prepared therefrom; and (7) miscellaneous film-forming materials such as silicone resins. The principles of pigmentation of this invention pertain also to durable, lightfast, transparent, low tinting strength, low hiding pigments other than the prime pigments which are shown as examples of the type most useful, namely; the hydrous iron oxides -#l and #16, the yellow #6, and the green #5, which contribute predominately to the transparency and outdoor durabilityof the products: Tinting andtoning pigments other th'an-violet-#2, blue #3, green #4 and maroon #11 will be found useful in the practice of this invention; and those listed are used to set forth the invention without limiting its scope.

Aluminum flake pigments 1 (extra fine), 8 (coarse) and 9 (fine) listed in Table 1- each contribute ;toa different degreeto the metallic appearance of a finished enamel. Pigment 8 (coarse) is preferred where the most brilliant metallic appearance is required. Pigment 9 (fine) givesa less brilliant eifect and #1 yieldsthe least brilliance of the threeylisted, although even enamels prepared from the latter are attractive and useful products. I I "It is obvious to one skilled in' the art that use.-

ful coating .compositions can be made within the scope of this invention using other primev or transparent base pigments, other tinting pigments, and other grades of aluminum pastes, resulting in the improvements set forth previously, although those used in this disclosure are currently preferred because the resulting colors are at present the most popular where metallic enamels are largely used-automobiles and certain other commercial articles.

The advantages of the enamels of this invention over conventional metallic coating compositions are depth, high-lighting of colors, ap-

parent color change when viewed from different directions or under difi'erent light, and polychromatic appearance; and, in addition to these, a marked improvement in outdoor durability over conventional metallic enamels in gloss retention, color retention, and general film integrity, including freedom from bronzing, chalking, checking, and cracking. The application properties and resistance to aluminum mottling of the metallic enamels of this invention are equal to, or better than, the duller and less brilliant conventional metallic enamels and are far superior to conventional products which have had large quantities of aluminum fiakes added to enhance th metallic 'efiect.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore, it is not intended to be limited except as indicated in the appended claims.

' I claim:

1.'Afc0ating composition adapted to yield a tough, durable finish having a metallic appearance of great depth and brilliance comprising a vehicle and pigment, the said pigment consisting of (A) prime pigment selected from material of the group consisting of colloidal hydrous iron oxide andchromium tetrahydroxide; (B) pigment substantially complementary in color to the said-prime pigment in amount to yield a gray when mixed separately therewith; (C) atleast onecolored tinting pigment and (D) finely divided flake-aluminum'metal. V

2. The composition of claim 1 in which the pigment (B) is a' lake of dichloroisodib'enzanthrone on barium rosinate.

3. The composition of claim 1 in which the pigmentKB) is phthalocyanine blue.

4."-1he composition of claim 1 in which the pigment(B) is phthalocyanine green.

5. The composition of claim 1 in which the pigment (B) is vat thioindigoid dyestuff-indo maroon.

6. The composition of claim 1 in which the aluminum flake is relatively coarse and about 40% of the total aluminum surface area is composed of flakes with a diameter larger than' 2O microns.

"7. The composition of claim 1 in which the pigment (A) is present in amount between 11% and 85.7% by weight of the total pigment; complementary pigment (B) and tinting pigment (0') combined are present in amount between 4.7% and 45%; and aluminum flakepowder (D) is present in amount between 4.5% and 36.4%.

8. The composition of claim 1 in which the vehicle contains a synthetic resin and the pig ments are present in amount as follows; 7

(A) 25 to 85.7 by Weight (B) and (c) 11% to 45% (D) 3.1% to 30% (A) 50.2% to 84.2% by weight (B) and (C) 4.7% to 44.6% (D) 4.5% 150 36.4%

10. The composition of claim 1 in which the pigment (B) is composed of a plurality of pigments, the resulting shade of which is substantially complementary to pigment (A).

11. The composition of claim 1 in which the pigment (B) is composed of a plurality of pigments, one of which is in excess of the amount necessary to produce a color complementary to pigment (A), the said excess being pigment (C).

12. The process of preparing coating compositions adapted to produce tough, durable finishes having a metallic appearance of great depth and brilliance which comprises blending (A) a relatively transparent pigmented composition, the pigment portion of which is selected from the group consisting of colloidal hydrous iron oxide and chromium tetrahydroxide; with (B) a pigmented composition in which the pigment is substantially complementary in color to the pigment of (A) tinting the resulting blend with (C) a colored pigmented composition and adding (D) a flake aluminum metal thereto.

13. The process of claim 12 in which the pigment (B) is a lake of dichloroisodibenzanthrone on barium rosinate.

14. The process of claim 12 in which the pigment (B) is phthalocyanine blue.

15. The process of claim 12 in which the pigment (B) isphthalocyanine green.

16. The composition of claim 12 in which the pigment (B) is vat thioindigoid dyestufi-indo maroon.

17. The process of claim 12 in which the alumi-- num flake is relatively coarse and about of the total aluminum surface area is composed of flakes with a diameter larger than 20 microns.

RALPH E. PIKE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS I Number Name Date 1,829,623 Wright Oct. 27, 1931 1,895,559 Straub et al. Jan. 31, 1933 1,974,745 Klinkenstein Sept. 25, 1934 2,062,137 McKinney et a1. Nov. 24, 1936 2,111,395 Hartwick Mar. 15, 1938 2,168,212 Hicks Aug. 1, 1939 2,178,018 Hofmann Oct. 31, 1939 2,185,293 Copeman Jan. 2, 1940 2,186,014 Ellis Jan. 9, 1940 2,343,925 Pike Mar. 14, 1944 2,405,953 Hillery Aug. 20, 1946 FOREIGN PATENTS Number Country Date 498,024 France Dec. 24, 1919 704,499 France May 20, 1931 877,582 France Dec. 10, 1942 

1. A COATING COMPOSITION ADAPTED TO YIELD A TOUGH, DURABLE FINISH HAVING A METALLIC APPEARANCE OF GREAT DEPTH AND BRILLIANCE COMPRISING A VEHICLE AND PIGMENT, THE SAID PIGMENT CONSISTING OF (A) PRIME PIGMENT SELECTED FROM MATERIAL OF THE GROUP CONSISTING OF COLLOIDAL HYDROUS IRON OXIDE AND CHROMIUM TETRAHYDROXIDE; (B) PIGMENT SUBSTANTIALLY COMPLEMENTARY IN COLOR TO THE SAID PRIME PIGMENT IN AMOUNT TO YIELD A GRAY WHEN MIXED SEPARATELY THEREWITH; (C) AT LEAST ONE COLORED TINTING PIGMENT AND (D) FINELY DIVIDED FLAKE ALUMINUM METAL. 